Granulocyte colony-stimulating factor (GCSF) is one of the hematopoietic growth factors with multifunctional activities. As a glycoprotein, GCSF plays important regulatory functions in the processes of maturation, proliferation, differentiation, and functional activation of granulocyte precursors and mature granulocytes in the bone marrow. It is able to augment white blood cell production when bone marrow dysfunction exists. Recombinant DNA technology has made it possible to clone the genes responsible for GCSF and to develop pharmaceutical products to treat a number of human hematopoietic conditions and disorders such as neutropenia and hematopietic stem cell transplantation.
Human GCSF (hGCSF) protein has a molecular mass of 19.6 kDa and exerts its biological functions through binding to the human GCSF receptor (hGCSFR), a single transmembrane protein with a large extracellular region that consists of an immunoglobulin-like (Ig-like) domain, a cytokine receptor homology (CRH) domain, and three fibronectin type III domains. Binding of GCSF to the extracellular Ig-like and CRH domains of the receptor triggers receptor homodimerization with a 2:2 stoichiometry of hGCSF/hGCSFR (Tamada T, et al. 2006 Homodimeric cross-over structure of the human GCSF receptor signaling complex. PNAS 103:3135-3140). The dimerization results in activation of intracellular Janus tyrosine kinase-signal transducers and activators of transcription (Jak-Stat) type signaling cascade. The signaling transfer of hematopoietic factor receptors from extracellular region to intracellular cascades has been suggested to be via conformational changes of the receptor dimer in TM domains. It has been demonstrated that the dimeric erythropoietin (EPO) receptor can be activated by mutations at the TM domain in the absence of the natural ligand EPO, a hematopoietic growth factor regulating red blood cell production (Lu X, et al. 2006 Active conformation of the erythropoietin receptor: Random and cycteine-scanning mutagenesis of the extracellular juxtamembrane and transmembrane domains. JBC 281:7002-7011). Patients with mutations in TM domain of hGCSFR have experienced chronic neutrophilia due to the receptor constitutive activation (Plo I, et al. 2009 An activating mutation in the CSF3R gene induces a hereditary chronic neutrophilia. JEM 206:1701-1707).
Several techniques for treating cancer are known in the art. Such techniques include, but are not limited to chemotherapy, radiation therapy, surgery, and transplantation. Many of these techniques, however, have undesirable side effects and varying success rates. Indeed, U.S. statistics for 2012 indicate that there will be an estimated 1,638,910 new cases of cancer (not including non-melanoma skin cancers) and 577,190 estimated deaths from cancer. Therefore, a need exists to develop new methods for treating cancer and/or diseases associated with cellular proliferation. While certain GCSF modulators have been clinically approved for the treatment of chemotherapy-induced neutropenia, thereby treating abnormally low numbers of neutrophils in a cancer patient, we have surprisingly discovered a new class of GCSF modulators that are cytotoxic to cancer cells.